Radio frequency (RF) sources, such as RF amplifiers, provide RF signals. When an RF signal generated by an RF source is provided to a load, such as to an antenna, a portion of the RF signal can be reflected back from the load. An electromagnetic (EM) coupler can be included in a signal path between the RF source and the load to provide an indication of forward RF power of the RF signal traveling from the RF source to the load and/or an indication of reverse RF power reflected back from the load. EM couplers include, for example, directional couplers, bi-directional couplers, multi-band couplers (e.g., dual band couplers), and the like.
An EM coupler typically has a power input port, a power output port, a coupled port, and an isolation port. When a termination impedance is presented to the isolation port, an indication of forward RF power traveling from the power input port to the power output port is provided at the coupled port. When a termination impedance is presented to the coupled port, an indication of reverse RF power traveling from the power output port to the power input port is provided at the isolation port. The termination impedance is typically implemented by a 50 Ohm shunt resistor in a variety of conventional EM couplers.
An EM coupler can provide forward or reverse coupled RF components of an RF signal entering the power input port or the power output port, respectively, which can be useful for, e.g., measuring the power of the RF signal. When the RF signal contains multiple frequency components, for instance from different bands or multiple frequencies within the same band, the coupled output of traditional EM couplers will include the multiple frequency components. This can cause power measurement equipment to indicate a higher power than is attributable to the frequencies of interest.